1. Field of the Invention
The present invention relates to a correction method of a position detector using a resolver and an electrically-powered steering apparatus for assisting steering of vehicle wheels based on a motor position detected by the position detector or a steering torque.
2. Description of Related Art
The electrically-powered steering apparatus, which is an important vehicle component, is demanded to have a high reliability. For the reason, public attention has been paid to a resolver-type position detector having a high mechanical reliability for detecting a steering torque of the electrically-powered steering apparatus and the motor position. As shown in FIG. 10, the resolver-type position detector comprises a resolver 40, an excitation signal generating circuit 32 for supplying an excitation signal of A0 θ sin ωt to the resolver 40, a resolver arithmetic processing I/F circuit 34 for amplifying cos phase signal (A0 cos θ sin ωt) acquired from the resolver 40, a resolver arithmetic processing I/F circuit 36 for amplifying sin phase signal (A0 sin θ cos ωt) acquired from the resolver 40 and a microcomputer 30 for computing a position from the sin phase and cos phase outputs of the resolver arithmetic processing I/F circuit 34 and the resolver arithmetic processing I/F circuit 36.
The structures of the resolver arithmetic processing I/F circuit 34 for amplifying the cos phase signal (A0 cos θ sin ωt) acquired from this resolver 40 and the resolver arithmetic processing I/F circuit 36 for amplifying the sin phase signal (A0 sin θ cos ωt) will be described with reference to FIG. 4. FIG. 4(A) shows the structure of the resolver arithmetic processing I/F circuit 34 and FIG. 4(B) shows the structure of the resolver arithmetic processing I/F circuit 36. The amplification factors of the resolver arithmetic processing I/F circuit 34 for amplifying the cos phase signal (A0 cos θ sin ωt) and the resolver arithmetic processing I/F circuit 36 for amplifying the sin phase signal (A0 sin θ cos ωt) are both R1/R2.
Here, if there is no deviation in resistance of each of the resolver arithmetic processing I/F circuit 34 and the resolver arithmetic processing I/F circuit 36, the amplification factors of the resolver arithmetic processing I/F circuit 34 and the resolver arithmetic processing I/F circuit 36 are equalized. However, actually there is produced a difference in the amplification factor depending on an error of resistance. If the position is computed from the sin phase and cos phase outputs based on this difference in the amplification factor by the microcomputer 30, an error of angle is generated.
Therefore, if the resolver-type position detector shown in FIG. 10 is employed as a motor angle sensor for the electrically-powered steering apparatus to control a brushless motor for assisting the steering of vehicle wheels, a torque ripple occurs so that steering feeling is lost. Further, if the resolver-type position detector is employed as a torque sensor for detecting a steering torque, a proper steering torque cannot be detected, so that the steering feeling is lost.